Five DNA viruses are known to cause cancers in humans. These are human papillomavirus, hepatitis B virus, Epstein-Barr virus, Kaposi sarcoma herpes virus and Merkel cell polyomavirus. It is estimated that, together, these are responsible for well over a million new cases of cancer worldwide annually. Also of interest is adenovirus: although it does not cause cancer in humans, it produces malignant tumours in experimental animals. This makes it a very powerful tool to study the mechanisms of viral oncogenesis. In recent years great strides have been made in our understanding of the molecular biology of these DNA viruses, and the virus-host interactions that drive carcinogenicity. These new data are essential first steps in the development of novel therapeutic strategies.

In this timely book, expert authors review the most important current research in this rapidly growing field. Topics covered range from an overview of the contribution of DNA tumour viruses to the cancer burden worldwide, and the molecular pathogenesis of virus driven cancers to vaccine development.

This volume will serve as a valuable reference source for everyone working in the field, both experts and students, in academia, government, and biotechnology companies. It is also a must-read for anyone with an interest in viral tumourigenesis and an important acquisition for all microbiology libraries.

Infections with certain infectious agents (viruses, bacteria, and parasites) have been identified as strong risk factors for specific cancers. Among those, four DNA viruses have been classified as carcinogenic to humans by IARC over the years: Hepatitis B virus (HBV) in 1994, 13 types of Human papillomaviruses (HPV) in 1995, Epstein Barr virus (EBV) and Kaposi sarcoma herpes virus (KSHV) in 1997. Numerous studies in humans, animals, and mechanistic evidences support a strong causal relationship between exposure to these four viruses and human cancer in at least one site, sometimes in several sites. Together, DNA viruses have been estimated to be responsible for 1.2 million new cases of cancer worldwide in 2012, with two viruses baring 85% of this burden: human papillomavirus (640 000 cases worldwide), and hepatitis B virus (420 000 cases). Most of the cancers due to DNA viruses occurred in Eastern Asia, Southern America, and sub-Saharan Africa, and 60% occurred in women. Merkel cell virus, another DNA virus, was discovered more recently in a rare skin cancer in human, and was classified as probably -but not definitively- carcinogenic to human by IARC in 2014 despite strong mechanistic evidence, due to the lack of prospective studies in human yet available. In this chapter we give an overview of the burden of cancers attributable to DNA viruses in the world and in eight geographical regions. Then we summarize for each infectious agent and cancer site, the body of epidemiological evidence supporting our estimates of the attributable fractions.

Human papillomaviruses (HPV) are small, double-stranded DNA viruses that replicate in squamous epithelium and cause hyperproliferative lesions, some of which are at risk of malignant transformation. The infectious HPV replication cycle is intimately linked to the differentiation program of this tissue. The virus infects undifferentiated basal keratinocytes to establish and maintain replication of the viral genome, whereas productive viral DNA amplification and formation of new progeny is restricted to differentiating keratinocytes. Successful viral replication in differentiated cells requires the virus to reprogram the post-mitotic keratinocytes in order to support viral genome replication. The use of animal PV models and cell-based tissue culture models of the virus life cycle, combined with generation of recombinant virions for infection studies, has revealed much about the complexities of the HPV life cycle. Defining the nature of the keratinocyte that HPV targets, infection strategies, and virus-host interactions necessary for virus DNA replication and virion production has contributed to the design of anti-HPV vaccines and the understanding of HPV-driven cancer development. This chapter aims to provide an overview of key HPV life cycle events and the models used to interrogate virus-host interplay.

The small double-stranded DNA human papillomaviruses (HPVs) form a family of approximately 200 viruses. They can infect the epithelia of the genital and upper respiratory tracts and the skin and are classified into several genera based on their DNA sequence. A small number belonging to genus alpha, referred to as mucosal high-risk (HR) HPV types, are clearly associated with human carcinogenesis. In particular, HR HPV16 and HPV18 are the most carcinogenic types, responsible for a large proportion of HPV-positive anogenital cancers. A vast number of studies have demonstrated that the products of two early genes, E6 and E7, play a key role in cellular transformation and cancer development. Both oncoproteins are very small molecules and do not have any enzymatic activities, but exert their biological properties by interacting with a large number of cellular proteins. These interactions result in modification of the activities of the cellular proteins, which, in some cases, are targeted to degradation via the proteasome pathway. The most studied examples are the ability of HR HPV E6 and E7 to induce degradation of p53 and pRb, respectively. Inactivation of these key tumour suppressors strongly alters cellular gene expression, leading to chromosomal instability and cellular transformation.

Despite the great knowledge of the biology of mucosal HR HPV types, additional research is needed to characterize the biology of the majority of HPV types that have been poorly investigated so far, with a final aim of evaluating their potential roles in other human diseases.

A chronic Hepatitis B Virus (HBV) infection can cause liver cancer, specifically hepatocellular carcinoma (HCC). A variety of mechanisms that can lead from HBV infection to development of HCC have been proposed and could include prolonged expression of HBV proteins that alter cellular signaling pathways, recurrent anti-HBV inflammatory responses associated with death of HBV-infected hepatocytes and concomitant liver regeneration, and integration of the HBV genome into the host cell chromosome, which could alter expression of cellular genes. Because it typically requires decades for a chronic HBV infection to cause liver cancer, it has been difficult to identify a single HBV-related effect that is carcinogenic, and it is likely that subtle HBV-associated effects over a prolonged period of time cause HCC. Anti-HBV therapies, such as interferon or nucleoside analogs can successfully control HBV replication and delay development of diseases associated with an HBV infection; however, these treatments are typically not curative. In this chapter, mechanisms that have been proposed to contribute to the progression and development of HBV-associated HCC, as well as established and emerging anti-HBV therapeutic strategies, will be discussed.

It is estimated that, globally, 15% of cancers can be attributed to viral infections. Hepatitis B virus (HBV) causes more than 300,000 cases of hepatocellular carcinoma per year and a subset of 13 human papillomaviruses (HPV) particularly HPV type 16 cause more than 530,000 cases of cervical cancer and 100,000 other anogenital and oropharyngeal cancers per year. HBV infection has been preventable by vaccination since 1982 and vaccination of neonates and infants is highly effective resulting already in decreased rates of new infections, chronic liver disease and HCC. Nonetheless HBV remains a global public health problem with high rates of vertical transmission from mother to child in some regions. Two prophylactic human papillomavirus (HPV) vaccines composed of virus like particles (VLPs) of the L1 capsid protein have been licensed since 2006/7. Both target infection by the oncogenic HPV's 16 and 18 (the cause of 70% of cervical cancers) and one also targets the low risk HPV types 6 and 11 that cause genital and laryngeal warts. The vaccines are now included in the national immunisation programmes in many countries, with young adolescent peri-pubertal girls the usual cohort for immunisation. Population effectiveness in women is now being demonstrated in countries with high vaccine coverage with significant reductions in cervical intra epithelial neoplasia, genital warts, vaccine HPV type genoprevalence and herd effects in young heterosexual men and older women. A third VLP vaccine targeting 7 oncogenic HPVs, 16, 18, 31, 33, 45, 52 and 58 plus HPV6 and 11 was licensed in the USA and Europe in 2014/2015 and it is predicted could reduce the incidence of cervical cancer by >85%.

Burkitt lymphoma (BL), first recognized by Denis Burkitt in 1958, is a high grade B cell malignancy particularly prevalent in young boys in tropical Africa and New Guinea. The high incidence of BL in areas of holo-endemic malaria prompted the search for a tumour-causing infectious agent transmitted by mosquitoes. This search, led by Anthony Epstein and co-workers, resulted in the discovery in cell lines derived from BL biopsies, of a gamma herpesvirus, later referred to as the Epstein-Barr virus (EBV). Subsequently, EBV was shown to be present in the tumour cells of patients with other forms of B cell lymphoma, such as Hodgkin lymphoma and post-transplant lymphoma, as well as in natural killer/T cell (NK/T) cell lymphomas and in several epithelial cancers such as nasopharyngeal carcinoma and gastric carcinoma. Understanding how EBV contributes to the development of these different forms of cancer has provided fundamental insights into the underlying mechanisms responsible for driving oncogenic processes as well as highlighting opportunities for prophylactic and therapeutic intervention. This chapter will summarise current knowledge of the role of EBV in lymphomagenesis, highlighting the importance of co-factors, including disorders of immunity, which can disrupt the delicate virus-host balance that otherwise ensures asymptomatic virus persistence in normal people.

While the contribution of Epstein-Barr virus (EBV) to the development of B cell tumours is well-studied, its precise role in the pathogenesis of epithelial cancers, such as nasopharyngeal carcinoma (NPC) and EBV-associated gastric cancer (EBVaGC), remains largely undefined. Most of our current understanding of the role of EBV in epithelial carcinogenesis comes from the studies on NPC because almost 98% of NPCs (compared to approximately 10% of gastric cancer) are EBV-positive. Indeed, many unique characteristics of NPC could be attributable to the virus and hence NPC is classified as a distinct type of head and neck cancer. Establishment of latent EBV infection in epithelial cells is thought to be an initiating event in preneoplastic cells, as well as the driving force for disease progression together with additional somatic changes as the tumour evolves. This chapter summarizes the major milestones in EBV research relating to epithelial cancers and describes some recent findings which help further our understanding of the role of EBV in epithelial carcinogenesis.

8. The Development of Prophylactic and Therapeutic Vaccines for Epstein-Barr Virus and its Associated Malignancies

Epstein-Barr virus (EBV), a member of the herpesvirus family, infects 90-95% of the world's population. Primary infection is usually silent but in some cases is associated with acute pathology that usually self-resolves. Following infection, EBV is carried for life as latent infection in memory B-cells with viral reactivation in the oropharynx generating infectious progeny for spread to new hosts. Although life-long infection with EBV is usually asymptomatic, the virus is associated with a range of lymphoid and epithelial cancers that total over 200,000 cases each year worldwide. Evidence that EBV infection is linked to autoimmune disorders, particularly multiple sclerosis, is also accumulating. Targeting the virus, by prophylactic or therapeutic vaccination, represents a rationale therapeutic strategy. This chapter focuses on the development of such vaccines, drawing parallels with other herpesviruses and other oncogenic viruses. The current status of EBV vaccine candidates and the signals of efficacy generated by laboratory studies and clinical trials are described.

Kaposi sarcoma herpesvirus (KSHV) is the causative agent of three malignancies, namely Kaposi sarcoma (KS), primary effusion lymphoma (PEL) and multicentric Castelman disease (MCD) and it is also the etiological agent of an inflammatory cytokine syndrome, KICS. In order to ensure its own survival and the successful accomplishment of its two modes of life cycle, a latent and a lytic phase, KSHV subverts several cellular processes. This chapter focuses on virus-host interactions that include manipulation of the cell cycle and apoptotic cascade, atypical differentiation of infected cells, aberrant angiogenesis and KSHV-induced metabolic alterations. By deregulating these cellular events, KSHV modulates the infected cell microenviroment and promotes viral tumourigenesis. Lastly, we present an overview of the current therapies for KSHV-associated malignancies and provide examples of how the study of KSHV molecular pathology could pave the way for new therapeutic approaches.

Merkel cell polyomavirus (MCPyV or MCV) is the first polyomavirus clearly shown to be associated with human cancer. Nearly all healthy adults asymptomatically shed MCPyV from their skin. In elderly and immunosuppressed individuals, infection can lead to a highly lethal form of skin cancer, Merkel cell carcinoma (MCC). Excessive exposure to sunlight and ultraviolet (UV) radiation, immune suppression, and advanced age are the most important risk factors for MCPyV-associated MCC. The incidence of MCC has tripled over the past two decades, and the concern for MCC grows as the aging population with prolonged sun exposure increases. With the high prevalence of MCPyV infection and an increasing amount of MCC diagnoses, there is a need to better understand the biology of MCPyV and its oncogenic potential. This chapter summarizes recent discoveries in MCPyV molecular virology, host cellular tropism, cell culture infection and animal models, and the unique genetic features of MCPyV that make it the only polyomavirus discovered to date that is associated with a human cancer. MCPyV is more likely to induce MCC in immunocompromised patients, thus providing an excellent probe for examining the role of the host immune system in controlling virus-induced oncogenesis. The interplay between MCPyV infection and host immune response and how disruption of this virus-host interaction may contribute to MCC pathogenesis is also reviewed. Together, our current knowledge provides a platform for future mechanistic studies to fully elucidate the MCPyV infectious life cycle and the mechanisms by which MCPyV infection contributes to MCC pathogenesis.

When viruses infect human cells, they must successfully resist host defences to faithfully replicate their genetic material. To do so, viruses interface with a number of cellular processes including the host DNA damage response. DNA viruses have a particularly precarious situation, in that they must infect cells without alerting the host DNA damage response pathway to recognize and launch a response against the viral DNA genome. This challenge has required DNA viruses to develop unique methods to allow the virus to interact with and evade the host DNA damage response. In this chapter, we focus on four DNA tumour viruses, Epstein-Barr virus (EBV), Kaposi sarcoma virus (KSHV), human papillomavirus (HPV), and adenovirus. These viruses modulate the DNA damage response by activating or deactivating sensors of DNA damage as well as key downstream effector molecules. Here we review the current literature discussing the integrated relationship between DNA tumour viruses and the host DNA damage response during lytic and latent viral infection.

Human adenoviruses were discovered through their ability to cause acute respiratory infections in people. Shortly thereafter, this human pathogen was additionally shown to have the capacity to induce malignant tumours when inoculated into experimental animals. By representing the first known tumourigenic human virus, adenovirus attracted many talented scientists to study its oncogenic properties. The resulting work demonstrated that adenovirus is a powerful tool for exposing general molecular mechanisms that commonly trigger the development of cancers. Another advancement stemming from these investigations was the adenovirus vector, which arose from technologies that allowed manipulation of the adenovirus genome and production of cell lines that stably express adenovirus genes. Considering the tumourigenic properties of human adenovirus, it may be somewhat surprising that adenovirus vectors are now employed to combat human cancers. The goal of this chapter is to review the molecular mechanisms discovered for the adenovirus oncogenes and the promise of adenovirus vectors as effective cancer therapeutics.